Vivaldi crashes when reopening from Dock

If I close the browser with the normal little red 'x' at the top left and try to reopen from the dock after a few minutes have elapsed, the app crashes. If I try this within a minute or so it will reopen normally. This is the same on three macs, two on 10.10.3 and one on Mavericks. This happens on a consistent basis. Edit: By 'reopen' I mean left click on the dock icon to open the app... if I right click the dock icon and click on 'open' in the pop up box the app opens fine.